// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_QUIC_QUIC_FLOW_CONTROLLER_H_
#define NET_QUIC_QUIC_FLOW_CONTROLLER_H_

#include "base/macros.h"
#include "net/base/net_export.h"
#include "net/quic/quic_protocol.h"

namespace net {

namespace test {
    class QuicFlowControllerPeer;
} // namespace test

class QuicConnection;

const QuicStreamId kConnectionLevelId = 0;

// QuicFlowController allows a QUIC stream or connection to perform flow
// control. The stream/connection owns a QuicFlowController which keeps track of
// bytes sent/received, can tell the owner if it is flow control blocked, and
// can send WINDOW_UPDATE or BLOCKED frames when needed.
class NET_EXPORT_PRIVATE QuicFlowController {
public:
    QuicFlowController(QuicConnection* connection,
        QuicStreamId id,
        Perspective perspective,
        QuicStreamOffset send_window_offset,
        QuicStreamOffset receive_window_offset,
        bool should_auto_tune_receive_window);

    ~QuicFlowController() { }

    // Called when we see a new highest received byte offset from the peer, either
    // via a data frame or a RST.
    // Returns true if this call changes highest_received_byte_offset_, and false
    // in the case where |new_offset| is <= highest_received_byte_offset_.
    bool UpdateHighestReceivedOffset(QuicStreamOffset new_offset);

    // Called when bytes received from the peer are consumed locally. This may
    // trigger the sending of a WINDOW_UPDATE frame using |connection|.
    void AddBytesConsumed(QuicByteCount bytes_consumed);

    // Called when bytes are sent to the peer.
    void AddBytesSent(QuicByteCount bytes_sent);

    // Set a new send window offset.
    // Returns true if this increases send_window_offset_ and is now blocked.
    bool UpdateSendWindowOffset(QuicStreamOffset new_send_window_offset);

    // Returns the current available send window.
    QuicByteCount SendWindowSize() const;

    // Send a BLOCKED frame if appropriate.
    void MaybeSendBlocked();

    // Returns true if flow control send limits have been reached.
    bool IsBlocked() const;

    // Returns true if flow control receive limits have been violated by the peer.
    bool FlowControlViolation();

    QuicByteCount bytes_consumed() const { return bytes_consumed_; }

    QuicStreamOffset highest_received_byte_offset() const
    {
        return highest_received_byte_offset_;
    }

    void set_receive_window_size_limit(QuicByteCount receive_window_size_limit)
    {
        DCHECK_GE(receive_window_size_limit, receive_window_size_limit_);
        receive_window_size_limit_ = receive_window_size_limit;
    }

    void set_auto_tune_receive_window(bool enable)
    {
        auto_tune_receive_window_ = enable;
    }

    // Should only be called before any data is received.
    void UpdateReceiveWindowSize(QuicStreamOffset size);

    bool auto_tune_receive_window() { return auto_tune_receive_window_; }

private:
    friend class test::QuicFlowControllerPeer;

    // Send a WINDOW_UPDATE frame if appropriate.
    void MaybeSendWindowUpdate();

    // Auto-tune the max receive window size.
    void MaybeIncreaseMaxWindowSize();

    // The parent connection, used to send connection close on flow control
    // violation, and WINDOW_UPDATE and BLOCKED frames when appropriate.
    // Not owned.
    QuicConnection* connection_;

    // ID of stream this flow controller belongs to. This can be 0 if this is a
    // connection level flow controller.
    QuicStreamId id_;

    // Tracks if this is owned by a server or a client.
    Perspective perspective_;

    // Tracks number of bytes sent to the peer.
    QuicByteCount bytes_sent_;

    // The absolute offset in the outgoing byte stream. If this offset is reached
    // then we become flow control blocked until we receive a WINDOW_UPDATE.
    QuicStreamOffset send_window_offset_;

    // Overview of receive flow controller.
    //
    // 0=...===1=======2-------3 ...... FIN
    //         |<--- <= 4  --->|
    //

    // 1) bytes_consumed_ - moves forward when data is read out of the
    //    stream.
    //
    // 2) highest_received_byte_offset_ - moves when data is received
    //    from the peer.
    //
    // 3) receive_window_offset_ - moves when WINDOW_UPDATE is sent.
    //
    // 4) receive_window_size_ - maximum allowed unread data (3 - 1).
    //    This value may be increased by auto-tuning.
    //
    // 5) receive_window_size_limit_ - limit on receive_window_size_;
    //    auto-tuning will not increase window size beyond this limit.

    // Track number of bytes received from the peer, which have been consumed
    // locally.
    QuicByteCount bytes_consumed_;

    // The highest byte offset we have seen from the peer. This could be the
    // highest offset in a data frame, or a final value in a RST.
    QuicStreamOffset highest_received_byte_offset_;

    // The absolute offset in the incoming byte stream. The peer should never send
    // us bytes which are beyond this offset.
    QuicStreamOffset receive_window_offset_;

    // Largest size the receive window can grow to.
    QuicByteCount receive_window_size_;

    // Upper limit on receive_window_size_;
    QuicByteCount receive_window_size_limit_;

    // Used to dynamically enable receive window auto-tuning.
    bool auto_tune_receive_window_;

    // Send window update when receive window size drops below this.
    QuicByteCount WindowUpdateThreshold();

    // Keep track of the last time we sent a BLOCKED frame. We should only send
    // another when the number of bytes we have sent has changed.
    QuicStreamOffset last_blocked_send_window_offset_;

    // Keep time of the last time a window update was sent.  We use this
    // as part of the receive window auto tuning.
    QuicTime prev_window_update_time_;

    DISALLOW_COPY_AND_ASSIGN(QuicFlowController);
};

} // namespace net

#endif // NET_QUIC_QUIC_FLOW_CONTROLLER_H_
